DevNet Associate (DEVASC) v1.0Network FundamentalsEasy
A network administrator is troubleshooting an issue where a newly deployed application on a server is unable to communicate with clients on a different subnet. The administrator suspects a firewall might be blocking the traffic. Which of the following TCP/IP layers is primarily responsible for filtering traffic based on port numbers?
- ANetwork Access layer
- BTransport layer
- CApplication layer
- DInternet layer
Show answer & explanationAnswer & explanation
Correct answer: B. Transport layer
The Transport layer, specifically TCP and UDP, uses port numbers to identify specific applications or services. Firewalls often inspect and filter traffic at this layer based on these port numbers.
Why the other options are wrong
- A. The Network Access layer (or Data Link/Physical layer) deals with physical addressing (MAC addresses) and media access, not port numbers.
- C. The Application layer deals with application-specific protocols and data formatting, not port-based filtering.
- D. The Internet layer (or Network layer) handles logical addressing (IP addresses) and routing, not port numbers.
TCP/IP Transport Layer
The TCP/IP Transport layer provides end-to-end communication between applications on different hosts, using protocols like TCP and UDP.
- Responsible for segmentation and reassembly of data.
- Uses port numbers to identify specific applications.
- TCP offers reliable, connection-oriented service; UDP offers unreliable, connectionless service.
Memory trick: Always Treat Internet Nuisances Seriously (Application, Transport, Internet, Network Access)